Method for dissolvable aluminum alloys

ABSTRACT

The method for equal channel angular extrusion increases yield strength and ultimate tensile strength of a dissolvable aluminum alloy. A billet of a dissolvable aluminum alloy is wrapped with a sheet cover so as to form a wrapped billet. The wrapped billet is extruded through an equal channel angular extrusion die with an extrusion angle ranging 90-135 degrees so as to form an extruded billet. The step of extruding is at a temperature ranging 150-250 degrees C., an extrusion rate ranging 0.003-0.010 inches per second, and a back pressure ranging 200-10000 psi. The dissolvable aluminum alloy of the extruded billet has a yield strength and ultimate tensile strength 50% greater than the initial yield strength and initial ultimate tensile strength.

CROSS-REFERENCE TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINTINVENTOR

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BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method to process dissolvablealuminum alloy. More particularly, the present invention relates to amethod for equal channel angular extrusion of the dissolvable aluminumalloy. Even more particularly, the present invention relates to a methodto modify dissolvable aluminum alloy in order to be suitable for formingdownhole components in the oil and gas industry.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 37 CFR 1.98.

Oil and gas production is commonly known to involve a borehole through aground formation with downhole tools, such as plugs and sleevespositioned along and within the borehole. The plugs close and openportions of the borehole so that a zone of ground formation can beisolated. A sleeve opens and closes to make the fluid connection betweenthe borehole and the ground formation. The downhole tools work toisolate and connect the zone for various operations to prepare andproduce the hydrocarbons from the ground formation. When the operationsare complete in the zone, components of the downhole tool or even theentire downhole tool may require removal. For example, a frac ball setin a plug to trigger a seal may be removed so that the seal is removed.Alternatively, the entire plug may be removed.

Dissolvable alloys were developed for the manufacture of downhole toolcomponents in the oil and gas industry. There are mainly two types ofdissolvable alloys: magnesium and aluminum based alloys. The dissolvablealuminum alloys typically have low ductility and low strength. Theadditives required for dissolvability negatively affect desirablephysical properties needed for downhole tool components. The additivesare low-melting-point elements, such as Ga, In and Sn, which reside atthe grain boundaries or produce the secondary phase particles in orderto create micro-scale galvanic corrosion with matrix materials. The lowmelting point alloys are dissolvable. However, there are difficultiesforming more complex shapes of components with low ductility, and thecomponents are not strong enough for downhole conditions of higherpressure and higher temperatures. The dissolvable aluminum alloys aretypically brittle after casting due to the existence of embrittlementelements with low melting points such as Ga, In or Sn. Therefore, theyare relatively difficult to be processed by traditional extrusionprocess.

There are prior art methods for post-processing casted dissolvablealuminum alloys. U.S. Pat. No. 8,211,248, issued on 3 Jul. 2012 toMarya, discloses heat treatment. Equal channel angular extrusion (ECAE)is another technique from the 1970′s known to increase the strength ofmetals and alloys.

Due to the intrinsic brittle nature of the dissolvable aluminum alloys,equal channel angular extrusion (ECAE) is not inherently compatible withdissolvable aluminum alloys. FIG. 2 shows that simply being adissolvable can result in a critical failure. FIG. 2 shows a comparisonthat the regular aluminum alloy 6061 (a) can be easily processed by ECAEwithout issue, while using the same ECAE conditions, a dissolvablealuminum alloy (b) fails.

It is an object of the present invention to provide a method forprocessing dissolvable aluminum alloy.

It is an object of the present invention to provide a method to improveductility and strength of a dissolvable aluminum alloy.

It is an object of the present invention to provide a method to modify adissolvable aluminum alloy for suitability for downhole tool components.

It is another object of the present invention to provide a method forequal channel angular extrusion compatible with dissolvable aluminumalloys.

These and other objectives and advantages of the present invention willbecome apparent from a reading of the attached specification.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include a method for equal channelangular extrusion. A billet of a dissolvable aluminum alloy is wrappedwith a sheet cover so as to form a wrapped billet. The dissolvablealuminum alloy has an initial strength and an initial tensileelongation. The method includes extruding the wrapped billet through anequal channel angular extrusion die with an extrusion angle ranging90-135 degrees so as to form an extruded billet. The step of extrudingis at a temperature ranging 150-250 degrees C., an extrusion rateranging 0.003-0.010 inches per second, and a back pressure ranging200-10000 psi. The dissolvable aluminum alloy of the extruded billet hasyield strength and ultimate tensile strength 50% greater than theinitial yield strength and ultimate tensile strength.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view of an equal channel angular extrusion method.

FIG. 2 are photos (a) and (b) of a regular aluminum alloy and adissolvable aluminum alloy after an equal channel angular extrusion inthe same conditions.

FIG. 3 are photos (a) and (b) of a dissolvable aluminum alloy after anequal channel angular extrusion in different temperature conditions.

FIG. 4 are photos (a) and (b) of a dissolvable aluminum alloy after anequal channel angular extrusion at different extrusion rates.

FIG. 5 are photos (a), (b), and (c) of a dissolvable aluminum alloyafter an equal channel angular extrusion at different back pressures.

FIG. 6 are photos (a) and (b) of a dissolvable aluminum alloy after anequal channel angular extrusion with and without wrapping materials.

FIG. 7 are photos (AA), (AC), (AG), and (AH) of four dissolvablealuminum alloys after an equal channel angular extrusion within thecritical range of conditions.

FIG. 8 are photos (a) and (b) of a dissolvable aluminum alloy before andafter an equal channel angular extrusion within the critical range ofconditions.

FIG. 9 is a graph illustration of tensile tests of dissolvable aluminumalloys before and after an equal channel angular extrusion within thecritical range of conditions.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-9 show the embodiments of the present invention as a method forequal channel angular extrusion of a dissolvable aluminum alloy withimproved yield strength and ultimate tensile strength. There is anincompatibility of dissolvable aluminum alloy with equal channel angularextrusion (ECAE) methods due to the very nature of the low melt elementsused for the dissolvability. As a material composition for downhole toolcomponents, the dissolvability cannot be eliminated. The dissolvabilityis the feature that is required of particular downhole tool components.FIG. 2 shows the critical limitation of the dissolvability. The regularaluminum alloy is easily processed without issue, while the dissolvablealuminum alloy is a complete failure. The dissolvable aluminum alloy canbe rendered non-functional by the ECAE method in FIG. 2.

FIG. 1 shows the method for equal channel angular extrusion. A billet 10is wrapped with a sheet cover 12 so as to form a wrapped billet. Thebillet 10 is comprised of a dissolvable aluminum alloy with an initialtensile yield strength, an initial tensile ultimate strength, and aninitial tensile elongation. The sheet cover 12 can be comprised of brassor graphite. The method includes extruding the wrapped billet through anequal channel angular extrusion die 20 with an extrusion angle 22ranging 90-135 degrees so as to form an extruded billet. The temperatureof the method can be controlled. FIG. 1 shows a pressing plunger 30 toset an extrusion rate by pressure P and a back plunger 32 to set a backpressure PB. Temperature, extrusion rate, back pressure, and wrappingare ECAE conditions that can affect the extruded aluminum alloy in theECAE method of the present invention

TABLE 1 results for temperature, extrusion rate, back pressure, andwrapping Back Temperature Extrusion Rate Pressure Critical FIG. (degreesC.) (inches/sec) (psi) Wrapping Fail 2 (a), 4(a) 250 0.01 200 YES YES 3(a) 100 0.005 200 YES YES 3 (b), 4 200 0.005 200 YES NO (b), 5 (a) 5 (b)200 0.005 4000 YES NO 5 (c) 200 0.005 8000 YES NO 6 (a) 330 0.005 0 NOYES 6 (b) 330 0.005 4000 YES NO 7-AA 200 0.005 8000 YES NO 7-AC 2000.005 8000 YES NO 7-AG 200 0.005 8000 YES NO 7-AH 200 0.005 8000 YES NO

There is a critical range of the temperature. FIG. 2-6 show thattemperatures both above and below 250 degrees can avoid fracturing ofthe extruded dissolvable aluminum alloy by an ECAE method. There is noteaching either way that higher or lower temperatures are better fordissolvable aluminum alloys. Furthermore, FIG. 2 shows that a lowertemperature can also be too low. Additionally, a higher temperature canalso be too high. A trial at 330 degrees C. avoided fracturing, but thedissolvable aluminum alloy over 400 degrees C. is already known to befracturing and non-functional based on known heat treatments at 400degrees C. There are critical ranges for temperature above and below 250degrees C., depending on other ECAE conditions.

There is a critical range of the extrusion rate. FIGS. 2-4 show thatslower extrusion rates can avoid fracturing of the extruded dissolvablealuminum alloy by an ECAE method. Even at extrusion rates slower than0.01 inches/sec, there can still be failure of the extruded dissolvablealuminum alloy. FIGS. 3 and 4 show that an extrusion rate lower than0.01 inches/sec can avoid fracturing, depending on temperature. There isno teaching that increasing extrusion rate above 0.01 inches per secondcan avoid fracturing, but it is known that increasing extrusion rate ismore likely to fail since the billet encounters less strain. When thereis already failure at 0.01 inches/sec, the teaching is to go slower.However, the present invention shows that going slower than 0.01inches/sec is not a guarantee to eventually avoid fracturing either.There is still a critical range for extrusion rate in FIGS. 2-4.

Back pressure can also be a critical ECAE condition. Table 1 showsfailures between 0-200 psi, while FIG. 5 shows that the back pressurefrom 200-8000 psi can avoid fracturing. A minimal back pressure at 200psi appears to be a critical pressure. Higher back pressures were alsoable to yield viable extruded dissolvable aluminum alloys after the ECAEprocess. The back pressure confines the material in the extrusionchamber in extrusion direction during the ECAP process, so that thematerial in the extrusion process will keep the integrity from alldirections.

FIG. 6 shows the benefit of wrapping to improve the ECAE process. Therecan be failures with or without wrapping. Embodiments of the presentinvention include the sheet cover of the wrapping material as brass,graphite or pure aluminum, which can act as a solid lubrication for thebillet 10 of dissolvable aluminum alloy. The results of Table 1 indicatethat wrapping is a critical ECAE condition with the extruded dissolvablealuminum alloy only avoiding fractures when wrapped.

Table 1 identifies the critical ranges as now claimed. The temperaturehas a range of 150-250 degrees C. with an extrusion rate range of0.003-0.010 inches per second and a back pressure range of 200-10000psi. Additionally, these conditions require wrapping. The presentinvention indicates the critical ranges interacting to avoid fracturesin the extruded dissolvable aluminum alloy.

Beyond achieving a functional extruded dissolvable aluminum alloy, themethod of the present invention further includes unexpected performance.Simply avoiding complete structural failure is important for componentsof downhole tools, but there is a further benefit beyond forming anextruded dissolvable aluminum alloy.

TABLE 2 results of FIG. 7 for increased strengths and sometimeselongation. Tensile Tensile Tensile Tensile Ultimate Ultimate TensileTensile Yield Strength Yield Strength Strength Strength ElongationElongation BEFORE AFTER BEFORE AFTER BEFORE AFTER Sample (MPa) (MPa)(MPa) (MPa) (%) (%) AA 137 275 190 325 3.3 8.7 AC 122 265 190 290 4.72.9 AG 153 273 187 320 1.4 2.1 AH 125 252 225 290 7.0 6.5

After identifying the ECAE conditions of the present invention,dissolvable aluminum materials were processed successfully, as shown inFIG. 7 and FIG. 8. The parts were processed without fractures that wouldrender the extruded dissolvable aluminum alloy unuseable. FIG. 8 showsan example of microstructural evolution during the ECAE process with8(a) showing a view before the ECAE process and 8(b) showing a viewafter the ECAE process. In the ECAE processed materials, there is lessmicro-porosity, and there is more even distribution of secondary phaseparticles. Micro-porosity and even distribution of secondary phaseparticles can contribute to the improvement of tensile mechanicalproperties. FIG. 9 shows the increased yield strength and ultimatetensile strength. Table 2 summarizes the improvement ranging 60-100% tosupport the unexpected 50% increase in yield strength and ultimatetensile strength of extruded dissolvable aluminum alloy.

In the present invention, just to achieve extruded dissolvable aluminumalloy that does not fracture is surpassed by the additional findings ofTable 2. There are actual improvements to mechanical properties beyondjust being able to form components of downhole tools without fractures.

The present invention provides a method for processing dissolvablealuminum alloy. After being cast, the dissolvable aluminum alloy must beformed into shapes that correspond to components of downhole tools.Being brittle makes the formation of parts difficult. Once formed, thecomponent must have the necessary strength for downhole conditions,while remaining dissolvable. The present invention improves thestrengths of a dissolvable aluminum alloy in a post processing treatmentof dissolvable aluminum alloy. Previously unusable or at least timeconsuming and expensive processing for downhole tool components can beavoided. The method for an equal channel angular extrusion has beenmodified to be compatible with dissolvable aluminum alloys. Regularalloys do not require such modifications, and there are critical rangesto avoid fracturing and failure of the extruded material. The presentinvention identifies these critical ranges to avoid failure and furtherachieves an unexpected improvement in strengths.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof. Various changes in the details ofthe illustrated structures, construction and method can be made withoutdeparting from the true spirit of the invention.

We claim:
 1. A method for equal channel angular extrusion, comprisingthe steps of: wrapping a billet with a sheet cover so as to form awrapped billet, said billet being comprised of a dissolvable aluminumalloy with an initial tensile yield strength; and extruding said wrappedbillet through an equal channel angular extrusion die with an extrusionangle ranging 90-135 degrees so as to form an extruded billet, whereinthe step of extruding is at a temperature ranging 150-250 degrees C.,wherein the step of extruding is at an extrusion rate ranging0.003-0.010 inches per second, wherein the step of extruding is at aback pressure ranging 200-10000 psi, and wherein said extruded billethas an extruded tensile yield strength 50% greater than said initialtensile yield strength.
 2. The method of claim 1, wherein saidtemperature is 200 degrees C.
 3. The method of claim 1, wherein saidextrusion rate is 0.005 inches per second.
 4. The method of claim 1,wherein said back pressure is 8000 psi.
 5. The method of claim 1,wherein said sheet cover is comprised of one of a group consisting ofbrass and graphite.
 6. A method for equal channel angular extrusion,comprising the steps of: wrapping a billet with a sheet cover so as toform a wrapped billet, said billet being comprised of a dissolvablealuminum alloy with an initial tensile ultimate strength; and extrudingsaid wrapped billet through an equal channel angular extrusion die withan extrusion angle ranging 90-135 degrees so as to form an extrudedbillet, wherein the step of extruding is at a temperature ranging150-250 degrees C., wherein the step of extruding is at an extrusionrate ranging 0.003-0.010 inches per second, wherein the step ofextruding is at a back pressure ranging 200-10000 psi, and wherein saidextruded billet has an extruded tensile ultimate strength 50% greaterthan said initial tensile ultimate strength.
 7. The method of claim 6,wherein said temperature is 200 degrees C.
 8. The method of claim 6,wherein said extrusion rate is 0.005 inches per second.
 9. The method ofclaim 6, wherein said back pressure is 8000 psi.
 10. The method of claim6, wherein said sheet cover is comprised of one of a group consisting ofbrass and graphite.
 11. A method for equal channel angular extrusion,comprising the steps of: wrapping a billet with a sheet cover so as toform a wrapped billet, said billet being comprised of a dissolvablealuminum alloy with an initial tensile elongation; and extruding saidwrapped billet through an equal channel angular extrusion die with anextrusion angle ranging 90-135 degrees so as to form an extruded billet,wherein the step of extruding is at a temperature ranging 150-250degrees C., wherein the step of extruding is at an extrusion rateranging 0.003-0.010 inches per second, wherein the step of extruding isat a back pressure ranging 200-10000 psi, and wherein said extrudedbillet has an extruded tensile elongation 50% greater than said initialtensile elongation.
 12. The method of claim 11, wherein said temperatureis 200 degrees C.
 13. The method of claim 11, wherein said extrusionrate is 0.005 inches per second.
 14. The method of claim 11, whereinsaid back pressure is 8000 psi.
 15. The method of claim 11, wherein saidsheet cover is comprised of one of group consisting of brass andgraphite.